The E89 has a much stronger chassis than the E85 where tower strut problems were commonplace ..deflection , cracking etc
AFAIK there are no support plates on common sale …if you are worried you could add a strut brace like Weicher across the struts that have substantial tower plates …
I’ve got one fitted although I can’t say I noticed any effect / improvement from its effect..
Bimmerworld did quite a bit of research on this and came to the conclusion that even on a track the later design of strut towers with their bracing were good…FWIW